Wafer to wafer structure and method of fabricating the same

ABSTRACT

A wafer to wafer structure includes a first wafer, a second wafer. A first bonding layer and a second bonding layer are disposed between the first wafer and the second wafer. A plurality of first interconnects are disposed within the he first bonding layer. A plurality of second interconnects are disposed within the second bonding layer. An interface is disposed between the first bonding layer and the second bonding layer. At least a through silicon via penetrates the first wafer, the first bonding layer and the interface to enter the second bonding layer. The through silicon via contacts one of the first interconnects and one of the second interconnects.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wafer to wafer structure and method of fabricating the same, and more particularly to a method and structure of coupling interconnects on different wafers using through silicon vias.

2. Description of the Prior Art

With increased requirements for chip density and smaller packaging form factors, advances have been made in three-dimensional integration of circuits. In this technology, devices are stacked, and bonded in the vertical direction. Typically, the stacked devices are electrically coupled by electrical contact pads on the devices.

A current flip-chip technique uses a direct electrical connection of face-down electronic components onto substrates, circuit boards, carriers or the like by means of conductive bumps on the chip bond pads. The flip-chip technique has a drawback in that the production efficiency is poor in terms of process complexity and product cost because it requires conventional solder-using complex connection processes. These are solder flux coating, chip/board arranging, solder bump ref lowing, flux removing, and curing processes.

It is desirable to have a novel method of fabricating stacked devices which involves easier processes.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a method of fabricating a wafer to wafer structure includes providing a first wafer covered by a first bonding layer, and a second wafer covered by a second bonding layer, wherein the first bonding layer comprises a plurality of first interconnects, and the second bonding layer comprises a plurality of second interconnects. The first bonding layer is mounted to the second bonding layer and an interface is disposed between the first bonding layer and the second bonding layer. Then, the first wafer is thinned. Finally, at least one through silicon via is formed to contact an interconnect of the first interconnects and an interconnect of the second interconnects.

According to another preferred embodiment of the present invention, a wafer to wafer structure includes a first wafer, a second wafer, a first bonding layer and a second bonding layer disposed between the first wafer and the second wafer, wherein the first bonding layer contacts the second bonding layer, an interface is disposed between the first bonding layer and the second bonding layer, a plurality of first interconnects are disposed within the first bonding layer, a plurality of second interconnects are disposed within the second bonding layer. At least one through silicon via penetrates the first wafer, the first bonding layer and the interface, and enters the second bonding layer, wherein the through silicon via contacts an interconnect of the first interconnects and an interconnect of the second interconnects.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 4 depict a method of fabricating a wafer to wafer structure according to a first preferred embodiment of the present invention.

FIG. 5 shows a variation of a wafer to wafer structure fabricated by the method of the first preferred embodiment of the present invention.

FIG. 6 depicts relative positions of interconnects.

FIG. 7 shows another variation of a wafer to wafer structure fabricated by the method of the first preferred embodiment of the present invention.

FIG. 8 shows yet another variation of a wafer to wafer structure fabricated by the method of the first preferred embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 to FIG. 4 depict a method of fabricating a wafer to wafer structure according to a first preferred embodiment of the present invention. As shown in FIG. 1, a first wafer 10 and a second wafer 30 are provided. A first bonding layer 12 covers the first wafer 10. The second bonding layer 32 covers the second wafer 30. Numerous first interconnects 14 are disposed within the first bonding layer 12 and numerous second interconnects 34 are disposed within the second bonding layer 32. The first wafer 10 and the second wafer 30 can independently include any semiconductor material, for example, Si, Ge, SiGe, SiC, SiGeC, Ga, GaAs, InAs or InP. Moreover, the first wafer 10 and the second wafer 30 may be doped, undoped or comprise both doped and undoped regions. The first wafer 10 may include at least one through silicon via (TSV) made by a TSV-first process. Similarity, the second wafer 30 may include at least one through silicon via made by a TSV-first process. The first bonding layer 12 and the second bonding layer 32 may independently include oxide, nitrogen-oxide, nitride or a combination thereof. The first interconnects 14 and the second interconnects 34 may independently include Al, Cu or other metals. The method of fabricating the first interconnects 14 in the first bonding layer 12, and the second interconnects 34 in the second bonding layer 32 may include etching the first bonding layer 12 and the second bonding layer 32 to form openings followed by depositing metals into the openings. Alternatively, the metals may be formed in advance then patterned, followed by forming the first bonding layer 12 and the second bonding layer 32 to cover the patterned metals. The steps of fabricating the first interconnects 14 and the second interconnects 34 may or may not be simultaneous. The first interconnects 14 may be formed before the second interconnects 34 or vice versa. Moreover, the first wafer 10 includes a front side 16 and a back side 18. The back side 18 is opposite the front side 16. The first bonding layer 12 covers and contacts the front side 16.

As shown in FIG. 2, the first bonding layer 12 is mounted on the second bonding layer 32. The first bonding layer 12 contacts the second bonding layer 32. The first bonding layer 12 is generally mounted on the second bonding layer 32 by an oxide fusion bonding process. In detail, the oxide fusion bonding process may include contacting and aligning the first bonding layer 12 to the second bonding layer 32 at room temperature. Then, the first bonding layer 12 and the second bonding layer 32 undergo a thermal anneal process at a temperature between 600 and 1200° C. for several hours to make the contact surface of the first bonding layer 12 and the second bonding layer 32 form chemical bonds to thereby complete the mounting. After the thermal anneal process, an interface is disposed between the first bonding layer 12 and the second bonding layer 32, wherein the interface is defined as a contact surface having chemical bonds between the first bonding layer 12 and the second bonding layer 32.

As shown in FIG. 3, the back side 18 of the first wafer 10 is thinned. As shown in FIG. 4, at least one through silicon via 40 is formed to penetrate the first wafer 10 from the back side 18, and penetrate the first bonding layer 12 and the interface 20. The through silicon via 40 enters the second bonding layer 32. The through silicon via 40 contacts an interconnect 14 a of the first interconnects 14 and an interconnect 34 a of the second interconnects 34. The through silicon via 40 may have two different types such as the through silicon via 40 a and the through silicon via 40 b. A suitable type of the through silicon via 40 can be decided based on different product requirements. As shown in FIG. 4, the through silicon via 40 a includes a first sub via 140, a second sub via 240 and a bridge 340, the first sub via 140 contacts the interconnect 14 a of the first interconnects 14, the second sub via 240 contacts the interconnect 34 a of the second interconnects 34, and the bridge 340 is disposed on the back side 18 of the first wafer 10 and contacts the first sub via 140 and the second sub via 240. In detail, the first sub via 140 penetrates the first wafer 10 and enters the first bonding layer 12, but the first sub via 140 does not penetrate the interface 20. The second sub via 240 penetrates the first wafer 10, the first bonding layer 12 and the interface 20 to enter the second bonding layer 32. The second sub via 240 does not enter the second wafer 30. The steps of fabricating the first sub via 140 and the second sub via 240 include etching the first wafer 10 to form two openings penetrating the first wafer 10 and entering the first bonding layer 12, wherein one of the openings takes the interconnect 14 a as an etching stop layer and will become the first sub via 140 later. Meanwhile, another opening (which will become the second sub via 240 later) continues to penetrate the first bonding layer 12, the interface 20, enter the second bonding layer 32 and take the interconnect 34 a as an etching stop layer. After that, two openings are filled with a metal layer, and the metal layer is also formed on the back side 18 of the first wafer 10. Then, the metal layer on the back side 18 of the first wafer 10 is patterned to form the bridge 340. Besides forming the bridge 340, the patterned metal layer on the back side 18 can also serve as a redistribution layer.

A bottom of the through silicon via 40 b has a step profile 440. The step profile 440 comprises a first plane surface 540 and a second plane surface 640, wherein the first plane surface 540 has a different height from that of the second plane surface 640. Preferably, the first plane surface 540 is higher than the second plane surface 640, but is not limited thereto. The first plane surface 540 contacts the interconnect 14 a of the first interconnects 14, and the second plane surface 640 contacts the interconnect 34 a of the second interconnects 34. The steps of fabricating the through silicon via 40 b include etching the first wafer 10 to form an opening penetrating the first wafer 10 and entering the first bonding layer 12. In the bonding layer 12, part of the opening takes the interconnect 14 a as an etching stop layer, and the remaining part of the opening which is not stopped by the interconnect 14 a continues to penetrate the interface 20, enter the second bonding layer 34 and stop on the interconnect 34 a. In other words, the interconnect 34 a serves as an etching stop layer for part of the opening. Later, a metal layer fills the opening and is formed on the back side 18 of the first wafer 10. Then, the metal layer on the back side 18 is patterned to form the through silicon via 40 b. The through silicon via 40 b does not enter the second wafer 30. The through silicon via 40 a and the through silicon via 40 b can be fabricated in the same step.

At this point, the interconnect 14 a of the first interconnect 14 electrically connects to the interconnect 34 a of the second interconnect 34 through the through silicon via 40 a or the through silicon via 40 b. A wafer to wafer structure 100 of the present invention is completed.

Although there are two through silicon vias 40 a and one through silicon via 40 b in the wafer to wafer structure 100, the number of through silicon vias 40 a and through silicon vias 40 b can be changed based on different requirements. For example, a wafer to wafer structure can utilize only the through silicon via 40 a to electrically connect the first interconnect 14 and the second interconnect 34 without using the through silicon via 40 b. In an alternative embodiment, as shown in FIG. 5, a wafer to wafer structure can utilize the through silicon via 40 b to electrically connect the first interconnect 14 and the second interconnect 34 without using the through silicon via 40 a. If the wafer to wafer structure does not need a redistribution layer at the back side 18, after the metal layer fills the opening, the metal layer on the back side 18 can be removed entirely by a chemical mechanical polish process, or other suitable process. After that, a surface 42 of the through silicon via 40 b aligns with the back side 18 of the first wafer 10.

It is noteworthy that the interconnect 14 a and the interconnect 34 a have specific relative positions, because the interconnect 14 a and the interconnect 34 a serve as etching stop layers when fabricating the through silicon via 40 a and the through silicon via 40 b. FIG. 6 depicts relative positions of the interconnect 14 a and the interconnect 34 a. For the sake of clarity, only the first wafer, 10, the second wafer 30, the interconnect 14 a, the interconnect 34 a, the first wafer 10, the second wafer 30, the first bonding layer 12, the interface 20 and the second bonding layer 32 are shown. There are three types of relative positions of the interconnect 14 a and the interconnect 34 a, which are designated here as type A, type B and type C, and shown in FIG. 6.

In relative position type A, the interconnect 14 a and the interconnect 34 a only partly overlap each other. In type B, the interconnect 34 a entirely overlaps the interconnect 14 a, and the interconnect 34 a is larger than the interconnect 14 a in the horizontal direction. In type C, the interconnect 14 a and the interconnect 34 a do not overlap each other. Type C is preferably used for the through silicon via 40 a. Furthermore, there is no other metal disposed between the interconnect 14 a and the interconnect 34 a in type A, type B and type C. In this way, the interconnect 14 a and the interconnect 34 a can be the etching stop layer when fabricating the through silicon via 40.

As shown in FIG. 7, the second wafer 30 can undergo the same processes illustrated in FIG. 1 to FIG. 5. The second wafer 30 can be thinned first. Then, a through silicon via 740 can be formed to penetrate the second wafer 30, the second bonding layer 32 and the interface 20, and enter the first bonding layer 12. At this point, a wafer to wafer structure with through silicon vias at two sides 200 is completed. The through silicon via 740 contacts an interconnect 14 b of the first interconnects 14 and an interconnect 34 b of the second interconnects 34. Similar to the through silicon via 40, the through silicon via 740 may also have two different types such as a through silicon via 740 a and a through silicon via 740 b. The structure of the through silicon via 740 a is the same as the through silicon via 40 a, and the through silicon via 740 b is the same as the through silicon via 40 b. The detailed description is therefore not repeated.

As shown in FIG. 8, after the wafer to wafer structure 100 is completed, a through silicon via 840 can be formed to penetrate the first wafer 10, the first bonding layer 12, the interface 20, the second bonding layer 32 and the second wafer 30 to align one end of the through silicon via 840 with the back side 18 of the first wafer 30. Furthermore, the other end of the through silicon via 840 is aligned with a back side 118 of the second wafer. At this point, a wafer to wafer structure 300 is completed.

FIG. 4 shows a wafer to wafer structure fabricated by the method illustrated in FIG. 1 to FIG. 4, wherein like reference numerals are used to refer to like elements throughout. A wafer to wafer structure 100 includes a first wafer 10 and a second wafer 30. A first bonding layer 12 and a second bonding layer 32 are disposed between the first wafer 10 and the second wafer 30, wherein the first bonding layer 12 contacts the second bonding layer 32. An interface 20 is disposed between the first bonding layer 12 and the second bonding layer 32. A plurality of first interconnects 14 are disposed within the first bonding layer 12. A plurality of second interconnects 34 are disposed within the second bonding layer 32. At least one through silicon via 40 penetrates the first wafer 10, the first bonding layer 12 and the interface 20, and enters the second bonding layer 32, wherein the through silicon via 40 contacts an interconnect 14 a of the first interconnects 14 and an interconnect 34 a of the second interconnects 34. The first wafer 10 comprises a front side 16 and a back side 18, the front side 16 is covered and contacted by the first bonding layer 12, and the back side 18 is opposite the front side 16. The through silicon via 40 may have two different types such as the through silicon via 40 a and the through silicon via 40 b. Suitable types of the through silicon via 40 can be decided based on different product requirements. The through silicon via 40 a includes a first sub via 140, a second sub via 240 and a bridge 340. The through silicon via 40 a includes a first sub via 140, a second sub via 240 and a bridge 340, the first sub via 140 contacts the interconnect 14 a of the first interconnects 14, the second sub via 240 contacts the interconnect 34 a of the second interconnects 34, and the bridge 340 is disposed on the back side 18 of the first wafer 10 and contacts the first sub via 140 and the second sub via 240. The first sub via 140 penetrates the first wafer 10 and enters the first bonding layer 12, but the first sub via 140 does not penetrate the interface 20. The second sub via 240 penetrates the first wafer 10, the first bonding layer 120 and the interface 20 to enter the second bonding layer 32. The second sub via 240 does not enter the second wafer 30. Moreover, a bottom of the through silicon via 40 b has a step profile 440. The step profile 440 comprises a first plane surface 540 and a second plane surface 640, wherein the first plane surface 540 has a different height from that of the second plane surface 640. Preferably, the first plane surface 540 is higher than the second plane surface 640, but is not limited thereto. The first plane surface 540 contacts the interconnect 14 a of the first interconnects 14, and the second plane surface 640 contacts the interconnect 34 a of the second interconnects 34. The through silicon via 40 b does not enter the second wafer 30.

As shown in FIG. 6, there are three types of relative positions of the interconnect 14 a and the interconnect 34 a, designated as type A, type B and type C. in type A, the interconnect 14 a and the interconnect 34 a only partly overlap each other. In type B, the interconnect 34 a entirely overlaps the interconnect 14 a, and the interconnect 34 a is larger than the interconnect 14 a in the horizontal direction. In type C, the interconnect 14 a and the interconnect 34 a do not overlap each other.

The wafer to wafer structures 100/200/300 of the present invention do not need bumps to electrically connect the first interconnects 14 to the second interconnect 34. Therefore, the fabricating steps do not need to include steps for making the bumps. Moreover, the first bonding layer 12 and the second bonding layer 32 are mounted together by the oxide fusion bonding process, and there is no bump on the first bonding layer 12 and the second bonding layer 32. Therefore, the contact surface between the first bonding layer 12 and the second bonding layer 32 is flat, and the mounting of the first bonding layer 12 and the second bonding layer 32 can be performed effectively.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. A wafer to wafer structure, comprising: a first wafer; a second wafer; a first bonding layer and a second bonding layer disposed between the first wafer and the second wafer, wherein the first bonding layer contacts the second bonding layer; an interface, disposed between the first bonding layer and the second bonding layer; a plurality of first interconnects disposed within the first bonding layer; a plurality of second interconnects disposed within the second bonding layer; and at least one through silicon via penetrating the first wafer, the first bonding layer and the interface, and entering the second bonding layer, wherein the through silicon via contacts an interconnect of the first interconnects and an interconnect of the second interconnects.
 2. The method of fabricating a wafer to wafer structure of claim 1, wherein the first wafer comprises a front side and a back side, the front side is covered and contacted by the first bonding layer, and the back side is opposite the front side.
 3. The method of fabricating a wafer to wafer structure of claim 2, wherein the through silicon via comprises a first sub via, a second sub via and a bridge, the first sub via contacts the interconnect of the first interconnects, the second sub via contacts the interconnect of the second interconnects, and the bridge is disposed on the back side and contacts the first sub via and the second sub via.
 4. The method of fabricating a wafer to wafer structure of claim 3, wherein the first sub via penetrates the first wafer and enters the first bonding layer, and the first sub via does not penetrate the interface, and wherein the second sub via penetrates the first wafer, the first bonding layer and the interface to enter the second bonding layer.
 5. The method of fabricating a wafer to wafer structure of claim 1, wherein a bottom of the through silicon via comprises a step profile, the step profile comprises a first plane surface and a second plane surface, the first plane surface has a different height from that of the second plane surface, the first plane surface contacts the interconnect of the first interconnects, and the second plane surface contacts the interconnect of the second interconnects.
 6. The method of fabricating a wafer to wafer structure of claim 1, wherein the interconnect of the first interconnects and the interconnect of the second interconnects do not overlap each other.
 7. The method of fabricating a wafer to wafer structure of claim 1, wherein the interconnect of the first interconnects and the interconnect of the second interconnects only partly overlap each other.
 8. The method of fabricating a wafer to wafer structure of claim 1, wherein the interconnect of the second interconnects entirely overlaps the interconnect of the first interconnects, and the interconnect of the second interconnects is larger than the interconnect of the first interconnects in a horizontal direction.
 9. The method of fabricating a wafer to wafer structure of claim 1, wherein both the first bonding layer and the second bonding layer are silicon oxide. 